We are presently isolating cDNA clones that encode the rat plasma membrane a-mannosidase that has previously been shown to be involved in sperm-egg interactions. Protein sequence data was obtained from the purified enzyme isolated from rat sperm plasma membranes. This protein sequence data is being used to isolate cDNA probes corresponding to the a-mannosidase coding region by degenerate PCR. Full-length cDNA clones will be subsequently isolated to determine the sequence, structure, substrate specificity, and molecular basis of the plasma membrane localization of this distinctive enzyme. These studies will eventually lead to an understanding of the role of this enzyme in fertilization in mammalian systems.